A significant percentage of people in the US have disorders of long-term memory; among these are people suffering from Alzheimer's disease (AD), posttraumatic stress disorder (PTSD), diabetes and depression. In addition to problems forming new memories, patients suffering from these diseases can have difficulty accessing older memories, especially in the advanced stages of the diseases, or-in the case of PTSD-patients may have difficulty regulating traumatic long-term memories. An important, and at present unresolved, question is the extent to which the memory difficulties experienced by some patients stem from retrieval problems or to degradation of the physical memory traces themselves. In order to answer this question, neuroscientists must learn more about how the brain maintains long-term memories. Contrary to long-held beliefs, older memories are not stable, even in healthy individuals, but, under some circumstances, can be rendered strikingly labile. Furthermore, once in this labile state the memories can become permanently disrupted. Two phenomena of long-term memory, termed memory reconsolidation and memory erasure, have attracted particular attention in this regard. Memory reconsolidation refers to the finding that, after having been given a reminder cue for a previously learned experience, a previously consolidated memory of that experience can become disrupted by treatments, such as exposure to inhibitors of protein synthesis, that interfere with original memory consolidation. So- called memory erasure has been observed following inhibition of a specific isoform of protein kinase C (PKC), known as PKM. PKM contains the catalytic domain of an atypical PKC, but lacks the regulatory domain and is therefore constitutively active. This property, it has been proposed, endows PKM with the capacity mediate memory maintenance. The phenomena of memory reconsolidation and memory erasure remain poorly understood and controversial. In part, these problems stem from the enormous complexity of the mammalian brain, as well as the complexity of the forms of memory that have been examined in studies of reconsolidation and memory erasure. This project will develop a simple model experimental system for a reductionist analysis of memory reconsolidation and memory erasure. The focus of the project will be on a nonassociative form of learning, long-term sensitization (LTS), in the marine snail, Aplysia. This organism offers several major advantages for the study of long-term memory maintenance, including the ability to investigate a form of long-term (>24 hr) synaptic plasticity, known as long-term facilitation, that unambiguously mediates the learning. The PI will use behavioral, cellular and molecular techniques to determine the neurobiological mechanisms that underlie memory reconsolidation and memory erasure. Data from the proposed studies will facilitate the development of treatments for disorders of long-term memory, including AD and PTSD.